Continuous improvements to bicycles are being sought in an attempt to maximize rider performance and comfort, increase durability of parts, reduce weight, etc. Numerous factors influence the overall performance of a bicycle, such as frame strength and weight, component weight, amount of suspension compression, etc. One factor which is of particular pertinence to bicycles having a rear wheel suspension is the frame geometry and that of the rear wheel suspension system. More particularly, small changes in the geometry of a rear wheel suspension system of a mountain bicycle frame, and particularly the relative position of the various pivot points thereof, can have quite significant effects on the performance of the suspension and thus the bicycle riding dynamics, resulting in changes in rider comfort, pedaling efficiency, amount of compression, handling characteristics, etc. There are numerous bicycle suspension systems in use today. Such suspension systems allow the rear wheel of the bike to better track the terrain resulting in improved traction while pedaling, turning, and braking. Additionally, the absorption of bump forces by the suspension system increases rider comfort. These systems range from the simple to the complex. Regardless of the type, rear wheel suspensions on pedal powered bicycles generally provide a rider with the benefits of a more comfortable ride and better control over the bicycle. Such bicycle suspension systems improve ride quality by absorbing the shocks incurred from encountering ground obstacles, rather than transmitting them through the frame to the rider.
For a suspension to be suitable for use on a bicycle, it must be efficient. Ideally, a perfect rear wheel suspension would compress only in reaction to ground forces but not to drive-train or braking forces. Unwanted suspension movement resulting from drive train forces wastes rider energy. Bicycle suspensions can be designed to react principally to ground forces, and such that drive-train and braking forces which act thereon are limited, by careful selection of suspension type and geometry.
However, as mountain bicycles become more and more designed for specific types of riding, such as downhill, cross-country, free ride, etc., the required geometries of the frame sets intended to be used for each of these types of riding are significantly different. This results in many different frame geometries being needed.
The designer of a bicycle frame set (ex: including a main frame and a rear wheel suspension system) is able to weigh the various desired riding characteristics of the bicycle being designed, based on intended use of the bicycle for example, and then design a suitable suspension geometry accordingly. However, once the bicycle and/or suspension geometry has been selected for any bicycle, short of completely changing components (such as type or length of shock absorber, etc.), the end user of the bicycle is not able to significantly change the geometry and therefore the characteristics of the bicycle frame set. However, the ability to modify the geometry of a bicycle remains desirable and confers the ability to potentially adapt the fabricated bicycle to many riders or for different terrains. Generally, the length of the tubes and the angles at which they are attached define the frame geometry. In rear wheel suspensions, the relative location of the pivot points will also have an impact on the frame geometry and overall characteristcs of the bicycle.
It would thus be advantageous to be able to readily modify the geometry of a bicycle and/or its rear wheel suspension, without having to change components, or change the entire bicycle frame in order to vary the riding characteristics of the bicycle.